Method of forming a semiconductor die with reduced RF attenuation

ABSTRACT

An electrically floating region is formed in the top surface of a semiconductor wafer to implement a radio frequency (RF) blocking structure. The RF blocking structure lies below the metal pads and traces that carry an RF signal in a metal interconnect structure to substantially reduces the attenuation of the RF signal.

This is a divisional application of application Ser. No. 11/900,467 filed on Sep. 12, 2007 now U.S. Pat. No. 7,598,575 by Jeffrey A. Babcock et al.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor die and, more particularly, to a semiconductor die with reduced RF attenuation.

2. Description of the Related Art

A semiconductor die is a well-known structure that includes a substrate material, such as single-crystal silicon, a metal interconnect structure that sits on top of the substrate material, and a number of electronic devices that are formed in and on the substrate material and/or in the metal interconnect structure. The metal interconnect structure electrically connects the electronic devices together to realize an electronic circuit.

FIG. 1 shows a perspective view that illustrates an example of a prior-art semiconductor die 100. As shown in FIG. 1, semiconductor die 100 includes a substrate material 110, and a metal interconnect structure 112 that sits on substrate material 110. Metal interconnect structure 112, in turn, includes a non-conductive material 114, and a number of layers of metal, including a top layer of metal, that are isolated by non-conductive material 114.

In the FIG. 1 example, only the top layer of metal is shown. In this example, the top layer of metal has a number of metal bond pads 120, including metal bond pad 120-1 and metal bond pad 120-2, and a number of metal traces 122, including metal trace 120-1 and metal trace 120-2, that extend away from the metal bond pads 120. Each metal bond pad 120 provides a point for an external electrical connection, while each metal trace 122 provides a signal path. Although not shown, the metal traces 122 are electrically connected to the electronic devices that are formed in and on substrate 110 material and/or in the metal interconnect structure 112.

In operation, when an RF signal is applied to metal bond pad 120-1, the RF signal propagates down metal trace 122-1. The RF signal on metal bond pad 120-1 and metal trace 122-1, in turn, is undesirably capacitively coupled to substrate material 110. In other words, as shown in FIG. 1, metal bond pad 120-1 and metal trace 122-1 function as the top plate of a parasitic capacitor 130, substrate material 110 functions as the bottom plate of parasitic capacitor 130, and non-conductive region 114 functions as the dielectric layer of parasitic capacitor 130.

Substrate material 110, in turn, is electrically conductive. As a result, as shown in FIG. 1, the RF signal capacitively coupled to substrate material 110 is also resistively coupled to a substrate bias node 132, such as ground, by a resistance 134. Thus, since a capacitor functions as a short circuit to a time varying signal, the RF signal is effectively connected to ground by way of resistance 134. As a result, a parasitic signal path exists from metal bond pad 120-1 and metal trace 120-1 to ground by way of capacitor 130 and resistance 134 that can significantly attenuate the RF signal propagating down metal trace 120-1.

In addition, the RF signal capacitively coupled to substrate material 110 is also resistively coupled to a region 136 of substrate 110 by a resistance 138. In region 136, the RF signal can be capacitively coupled to metal bond pad 120-2 and metal trace 122-2 by way of a parasitic capacitor 140.

As a result, a second parasitic signal path exists from metal bond pad 120-1 and metal trace 122-1 to metal bond pad 120-2 and metal trace 122-2 by way of capacitor 130, resistance 138, and capacitor 140 that can significantly attentuate the RF signal. Further, an RF signal capacitively coupled to metal bond pad 120-2 and metal trace 122-2 by way of parasitic capacitor 140 degrades and interferes with an RF signal that is placed on metal bond pad 120-2 and metal trace 122-2. One approach to reducing the attenuation associated with the parasitic signal paths is to increase the thickness (height) of non-conductive material 114 so that metal bond pad 120-1 and metal trace 122-1 lie further away from the top surface of substrate material 110. Another approach is to reduce the coupling area by reducing the widths of the metal traces. A further approach is to utilize a high-resistance substrate material that has the effect of substantially increasing the values of resistance 134 and resistance 138.

Although each of these approaches provides some reduction in the attenuation of an RF signal, there is a need for an additional approach to reducing the attenuation of an RF signal that propagates down a metal trace of a metal interconnect structure after being applied to a metal bond pad.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of a prior-art semiconductor die 100.

FIGS. 2A-2B are views illustrating an example of a semiconductor die 200 in accordance with the present invention. FIG. 2A is a plan view. FIG. 2B is a cross-sectional view taken along lines 2B-2B of FIG. 2A.

FIGS. 3A-3B are views illustrating an example of a semiconductor die 300 in accordance with the present invention. FIG. 3A is a plan view, while FIG. 3B is a cross-sectional view taken along lines 3B-3B of FIG. 3A.

FIGS. 4A-4B are views illustrating an example of a semiconductor die 400 in accordance with the present invention. FIG. 4A is a plan view. FIG. 4B is a cross-sectional view taken along lines 4B-4B of FIG. 4A.

FIGS. 5A-5B are views illustrating an example of a semiconductor die 500 in accordance with the present invention. FIG. 5A is a plan view. FIG. 5B is a cross-sectional view taken along lines 5B-5B of FIG. 5A.

FIGS. 6A-6B are views illustrating an example of a semiconductor die 600 in accordance with the present invention. FIG. 6A is a plan view. FIG. 6B is a cross-sectional view taken along lines 6B-6B of FIG. 6A.

FIGS. 7A-7B are views illustrating an example of a semiconductor die 700 in accordance with the present invention. FIG. 7A is a plan view. FIG. 7B is a cross-sectional view taken along lines 7B-7B of FIG. 7A.

FIGS. 8A-8B are views illustrating a further example of the semiconductor dice 200-700 in accordance with the present invention. FIG. 8B is a cross-sectional view. FIG. 8A is a plan view taken along lines 8A-8B of FIG. 8B.

FIGS. 9A-9B are views illustrating an additional example of the semiconductor dice 200-700 in accordance with the present invention. FIG. 9B is a cross-sectional view. FIG. 9A is a plan view taken along lines 9A-9B of FIG. 9B.

FIGS. 10A-10I are cross-sectional views illustrating an example of a method of forming a semiconductor die in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 2A-2B are views that illustrate an example of a semiconductor die 200 in accordance with the present invention. FIG. 2A shows a plan view, while FIG. 2B shows a cross-sectional view taken along lines 2B-2B of FIG. 2A. As described in greater detail below, semiconductor die 200 includes a number of RF blocking structures that reduce the attenuation of an RF signal.

As shown in FIGS. 2A-2B, semiconductor die 200 includes a p− substrate material 210, such as p− single-crystal silicon or a p− epitaxial layer, and a number of spaced-apart RF blocking structures 212 that are formed in substrate material 210. The RF blocking structures 212, in turn, include a number of isolation rings 214 such that each RF blocking structure 212 has an isolation ring 214. In addition, each isolation ring 214 includes a shallow trench isolation ring 216 and a deep trench isolation ring 218.

The RF blocking structures 212 also include a number of floating n− wells 220 that are formed in p− substrate material 210 such that each RF blocking structure has a floating n− well 220. A floating n− well 220 is defined to be an n− well that receives no external bias voltage. In the present example, the floating n− wells 220 do not touch any metal contact structures and, therefore, are never externally biased. Further, the n− wells 220 are formed in p− substrate material 210 such that each isolation ring 214 laterally surrounds an n− well 220. In the present example, no p-type region is formed in any n− well 220.

As further shown in FIGS. 2A-2B, the RF blocking structures 212 include a number of space-charge depletion regions 222 such that each RF blocking structure 212 includes a space-charge depletion region 222. The space-charge depletion region 222 of an RF blocking structure 212 extends into p− substrate material 210 and the n− well 220 of the RF blocking structure 212.

Semiconductor die 200 additionally includes a metal interconnect structure 224 that sits on the top surface of p− substrate material 210. Metal interconnect structure 224, in turn, includes a non-conductive structure 226 (which can include a number of separate non-conductive layers of the same or different materials), and a number of layers of metal, including a top layer of metal, that are isolated by non-conductive structure 226.

In the FIGS. 2A-2B example, only the top layer of metal is shown. In this example, the top layer of metal has a number of metal bond pads, including metal bond pad 230, and a number of metal traces, including metal trace 232, that extend away from the metal bond pads. Each metal bond pad provides a point for an external electrical connection, while each metal trace provides a signal path. Although not shown, the metal traces are electrically connected to devices that are formed in and on substrate material 210 and/or in the metal interconnect structure 224.

In operation, when an RF signal is applied to metal bond pad 230, the RF signal propagates down metal trace 232. As with semiconductor die 100, the RF signal on metal bond pad 230 and metal trace 232 of semiconductor die 200 is undesirably capacitively coupled to substrate material 210. In addition, the RF signal capacitively coupled to substrate material 210 is also resistively coupled to a substrate bias node and to other regions of substrate material 210.

In accordance with the present invention, by locating an array of RF blocking structures 212 directly below the metal bond pads 230 and the metal traces 232, the attenuation of the RF signal is reduced. Simulation results indicate an improvement of approximately 0.5 dB. In addition to the metal bond pads 230 and the metal traces 232, the RF blocking structures 212 can also be located directly below other devices that the RF signal passes through, such as an inductor and a capacitor of a passive equalizer that are formed in metal interconnect structure 224.

It is believed that the reduced attenuation results from the disruption of magnetically-induced eddy currents along the top surface of substrate material 210. For example, the isolation rings 214 block large eddy currents from forming along the top surface of substrate material 210, while the space-charge depletion regions 222 further reduce the formation of eddy currents.

FIGS. 3A-3B are views that illustrate an example of a semiconductor die 300 in accordance with the present invention. FIG. 3A shows a plan view, while FIG. 3B shows a cross-sectional view taken along lines 3B-3B of FIG. 3A. Semiconductor die 300 is similar to semiconductor die 200 and, as a result, utilizes the same reference numerals to designate the structures which are common to both dice.

As shown in FIGS. 3A-3B, semiconductor die 300 differs from semiconductor die 200 in that die 300 utilizes a number of RF blocking structures 312 in lieu of the RF blocking structures 212. The RF blocking structures 312, in turn, are similar to the RF blocking structures 212 and, as a result, utilize the same reference numerals to designate the elements which are common to both structures.

As further shown in FIGS. 3A-3B, the RF blocking structures 312 differ from the RF blocking structures 212 in that each RF blocking structure 312 also includes a floating p-type grid 314 that is formed in n− well 220, and a space-charge depletion region 316 that extends into n− well 220 and p-type grid 314. A floating p-type grid 314 is defined to be a p-type grid that receives no external bias voltage. In the present example, no floating p-type grid 314 touches any metal contact structure and, therefore, is never externally biased.

Each grid 314 is illustrated with a “+” shape that separates n− well 220 into four equally-sized cells for the sake of clarity, and can include a larger grid with additional cells of the same or different sizes. Further, a p-type grid 314 can have the same dopant concentration as substrate material 210, or a different, e.g., greater, dopant concentration than substrate material 210.

In operation, the presence of a p-type grid 314 in each RF blocking structure 312 limits the formation of any eddy currents that are larger than a grid cell, and allows the formation of a space-charge depletion region 316 in each RF blocking structure 312 that is in addition to space-charge depletion region 222. As a result, the combination of space-charge depletion region 222 and space-charge depletion region 316 in each RF blocking structure 312 further inhibits the formation of eddy currents.

FIGS. 4A-4B are views that illustrate an example of a semiconductor die 400 in accordance with the present invention. FIG. 4A shows a plan view, while FIG. 4B shows a cross-sectional view taken along lines 4B-4B of FIG. 4A. Semiconductor die 400 is similar to semiconductor die 200 and, as a result, utilizes the same reference numerals to designate the structures which are common to both dice.

As shown in FIGS. 4A-4B, semiconductor die 400 differs from semiconductor die 200 in that die 400 utilizes a number of RF blocking structures 412 in lieu of the RF blocking structures 212. The RF blocking structures 412, in turn, are similar to the RF blocking structures 212 and, as a result, utilize the same reference numerals to designate the elements which are common to both structures.

As further shown in FIGS. 4A-4B, the RF blocking structures 412 differ from the RF blocking structures 212 in that each RF blocking structure 412 also includes a number of spaced-apart floating p-type regions 414 that are formed in n− well 220, and a number of space-charge depletion regions 416 that extend into n− well 220 and the p-type regions 414. A floating p-type region 414 is defined to be a p-type region that receives no external bias. In the present example, the floating p-type regions 414 do not touch any metal contact structure and, therefore, are never externally biased. Further, a p-type region 414 can have the same dopant concentration as substrate material 210, or a different, e.g., greater, dopant concentration than substrate material 210.

In operation, the presence of the p-type regions 414 in each RF blocking structure 412 allows the formation of the space-charge depletion regions 416 in each RF blocking structure 412 that are in addition to space-charge depletion region 222. As a result, the combination of space-charge depletion region 222 and the space-charge depletion regions 416 in each RF blocking structure 412 further inhibits the formation of eddy currents.

FIGS. 5A-5B are views that illustrate an example of a semiconductor die 500 in accordance with the present invention. FIG. 5A shows a plan view, while FIG. 5B shows a cross-sectional view taken along lines 5B-5B of FIG. 5A. Semiconductor die 500 is similar to semiconductor die 200 and, as a result, utilizes the same reference numerals to designate the structures which are common to both die.

As shown in FIGS. 5A-5B, semiconductor die 500 differs from semiconductor die 200 in that die 500 utilizes a number of RF blocking structures 512 in lieu of the RF blocking structures 212. The RF blocking structures 512, in turn, are similar to the RF blocking structures 212 and, as a result, utilize the same reference numerals to designate the elements which are common to both structures.

As further shown in FIGS. 5A-5B, the RF blocking structures 512 differ from the RF blocking structures 212 in that each RF blocking structure 512 utilizes a floating n− well 520 in lieu of floating n− well 220, a space-charge depletion region 522 in lieu of space-charge depletion region 222, and a p-type ring 524 that lies between n− well 520 and isolation ring 214. A floating n− well 520 is defined to be an n− well that receives no external bias. In the present example, the floating n− wells 520 do not touch any metal contact structure and, therefore, are never externally biased. In addition, no p-type region is formed in any n− well 520. A p-type ring 524 can have the same dopant concentration as substrate material 210, or a different, e.g., greater, dopant concentration than substrate material 210.

In operation, the presence of a p-type ring 524 in each RF blocking structure 512 allows the formation of a space-charge depletion region 522 in each RF blocking structure 512 that is larger than a space-charge region 222. As a result, the larger space-charge depletion region 522 in each RF blocking structure 512 further inhibits the formation of eddy currents.

FIGS. 6A-6B are views that illustrate an example of a semiconductor die 600 in accordance with the present invention. FIG. 6A shows a plan view, while FIG. 6B shows a cross-sectional view taken along lines 6B-6B of FIG. 6A. Semiconductor die 600 is similar to semiconductor die 500 and, as a result, utilizes the same reference numerals to designate the structures which are common to both dice.

As shown in FIGS. 6A-6B, semiconductor die 600 differs from semiconductor die 500 in that die 600 utilizes a number of RF blocking structures 612 in lieu of the RF blocking structures 512. The RF blocking structures 612, in turn, are similar to the RF blocking structures 512 and, as a result, utilize the same reference numerals to designate the elements which are common to both structures.

As further shown in FIGS. 6A-6B, the RF blocking structures 612 differ from the RF blocking structures 512 in that each RF blocking structure 612 also includes a floating p-type grid 614 that is formed in n− well 520, and a space-charge depletion region 616 that extends into n− well 520 and p-type grid 614. A floating p-type grid 614 is defined to be a p-type grid that receives no external bias. In the present example, no floating p-type grid 614 touches any metal contact structure and, therefore, is never externally biased.

Each grid 614 is illustrated with a “+” shape that separates n− well 520 into four equally-sized cells for the sake of clarity, and can include a larger grid with additional cells of the same or different sizes. Further, a p-type grid 614 can have the same dopant concentration as substrate material 210, or a different, e.g., greater, dopant concentration than substrate material 210.

In operation, the presence of a p-type grid 614 in each RF blocking structure 612 limits the formation of any eddy currents that are larger than a grid cell, and allows the formation of a space-charge depletion region 616 in each RF blocking structure 612 that is in addition to space-charge depletion region 522. As a result, the combination of space-charge depletion region 522 and space-charge depletion region 616 in each RF blocking structure 612 further inhibits the formation of eddy currents.

FIGS. 7A-7B are views that illustrate an example of a semiconductor die 700 in accordance with the present invention. FIG. 7A shows a plan view, while FIG. 7B shows a cross-sectional view taken along lines 7B-7B of FIG. 7A. Semiconductor die 700 is similar to semiconductor die 500 and, as a result, utilizes the same reference numerals to designate the structures which are common to both dice.

As shown in FIGS. 7A-7B, semiconductor die 700 differs from semiconductor die 500 in that die 700 utilizes a number of RF blocking structures 712 in lieu of the RF blocking structures 512. The RF blocking structures 712, in turn, are similar to the RF blocking structures 512 and, as a result, utilize the same reference numerals to designate the elements which are common to both structures.

As further shown in FIGS. 7A-7B, the RF blocking structures 712 differ from the RF blocking structures 512 in that each RF blocking structure 712 also includes a number of spaced-apart floating p-type regions 714 that are formed in n− well 520, and a number of space-charge depletion regions 716 that extend into n− well 520 and the p-type regions 714. A floating p-type region 714 is defined to be a p-type region that receives no external bias. In the present example, the floating p-type regions 714 do not touch any metal contact structure and, therefore, are never externally biased. Further, a p-type region 714 can have the same dopant concentration as substrate material 210, or a different, e.g., greater, dopant concentration than substrate material 210.

In operation, the presence of the p-type regions 714 in each RF blocking structure 712 allows the formation of the space-charge depletion regions 716 in each RF blocking structure 712 that are in addition to space-charge depletion region 522. As a result, the combination of space-charge depletion region 522 and the space-charge depletion regions 716 in each RF blocking structure 712 further inhibits the formation of eddy currents.

FIGS. 8A-8B are views that illustrate a further example of the semiconductor dice 200-700 in accordance with the present invention. FIG. 8B shows a cross-sectional view. FIG. 8A shows a plan view taken along lines 8A-8B of FIG. 8B. In the present invention, the semiconductor dice 200-700 can be implemented with the conductivity types reversed, for example, utilizing an n− substrate material, p− wells, and n-type grids and spaced-apart regions.

As shown in FIGS. 8A-8B, the semiconductor dice 200-700 can each have a p− substrate 810, such as single-crystal silicon, that contacts and lies below n− substrate material 210, and a number of spaced-apart n+ buried regions 812 that are formed in p− substrate 810. The n+ buried regions 812 also contact n− substrate material 210. The semiconductor dice 200-700 can each also have a number of space-charge depletion regions 814 that extend into p− substrate 810 and the n+ buried regions 812.

In operation, the presence of the n+ buried regions 812 below the isolation rings 214 allows the formation of the space-charge depletion regions 814 that are in addition to the previously discussed space-charge depletion regions of the dice 200-700. As a result, the addition of the space-charge depletion regions 814 to the previously-described space-charge depletion regions of the dice 200-700 further inhibits the formation of eddy currents.

FIGS. 9A-9B are views that illustrate an additional example of the semiconductor dice 200-700 in accordance with the present invention. FIG. 9B shows a cross-sectional view. FIG. 9A shows a plan view taken along lines 9A-9B of FIG. 9B. As shown in FIGS. 9A-9B, the semiconductor dice 200-700 can each have a p− substrate 910, such as single-crystal silicon, that contacts and lies below n− substrate material 210, and an n+ grid 912 that is formed in p− substrate 910. N+ grid 912 also contacts n− substrate material 210. The semiconductor dice 200-700 can each also have a space-charge depletion region 914 that extends into p− substrate 910 and n+ grid 912.

In operation, the presence of n+ grid 912 below the isolation rings 214 limits the formation of any eddy currents that are larger than a grid cell, and allows the formation of a space-charge depletion region 914 that is in addition to the previously discussed space-charge depletion regions of dice 200-700. As a result, the addition of space-charge depletion region 914 to the previously-discussed space-charge depletion regions of dice 200-700 further inhibits the formation of eddy currents.

FIGS. 10A-10I are cross-sectional views that illustrate an example of a method of forming a semiconductor die in accordance with the present invention. As shown in FIG. 10A, the method utilizes a conventionally-formed wafer that includes a p− substrate material 1010, such as p− single-crystal silicon or a p− epitaxial layer, and a number of spaced-apart dummy composite structures 1012 that are formed in substrate material 1010.

As further shown in FIG. 10A, the dummy composite structures 1012 include a number of isolation rings 1014 such that each dummy composite structure 1012 has an isolation ring 1014. In addition, each isolation ring 1014 includes a shallow trench isolation ring 1016 and a deep trench isolation ring 1018.

The wafer includes both active composite structures and dummy composite structures. Transistors and other devices are formed in the active composite structures of the wafer, while nothing is formed in the dummy composite structures. (In some prior-art fabrication processes, the dummy composite structures are implanted with a dopant (p-type in the present example) of the same conductivity type as the substrate material.)

Dummy composite structures are commonly formed in the inactive regions of a wafer, and serve to minimize dishing when the top surface of the substrate region is chemically-mechanically polished following the formation of the isolation rings 1014. In accordance with the present invention, an array of dummy composite structures 1012 are formed directly below where the RF metal bond pads, the RF metal traces, and the RF devices (e.g., the inductors) are to be formed.

Referring again to FIG. 10A, the method begins by forming and patterning a mask 1020 on the top surface of p− substrate material 1010. Following this, the wafer is implanted with an n-type dopant to form a number of n− wells 1022 such that an n− well 1022 lies inside the isolation ring 1014 of each dummy composite structure 1012.

In addition, a space-charge depletion region 1024 is formed along the junction between each n-well 1022 and the substrate material 1010. (A space-charge depletion region is formed whenever an n-type material is brought into contact with a p− type material.) As shown, the implant forms a number of RF blocking structures 1026, like RF blocking structures 212. Mask 1020 is then removed.

Next, as shown in FIG. 10B, a metal interconnect structure 1030 is conventionally formed on the top surface of p− substrate material 1010 so that no portion of the n− wells 1022 is electrically connected to metal interconnect structure 1030. Metal interconnect structure 1030 includes a non-conductive structure 1032, such as a number of layers of oxide and nitride, that touches the top surface of p− substrate material 1010, and a top metal layer that includes a metal structure 1034, such as a metal bond pad or a metal trace.

Alternately, as shown in FIG. 10C, after the n− wells 1022 have been formed and mask 1020 has been removed, a mask 1040 can be formed and patterned on the top surface of p− substrate material 1010. Following this, the wafer is implanted with a p-type dopant to form a number of p+ structures 1042 so that a p+ structure 1042 lies inside each n− well 1022. The p+ structures 1042 can be formed as a grid (to form a number of RF blocking structures 312) or as a number of spaced-apart regions (to form a number of RF blocking structures 412). Mask 1040 is then removed, followed by the conventional formation of metal interconnect structure 1030.

Alternately, rather than patterning mask 1020 as shown in FIG. 10A, mask 1020 can be patterned as shown in FIG. 10D to protect a peripheral region of each RF blocking structure. Following this, the wafer is implanted with an n-type dopant to form an n− well 1044 that lies inside the isolation ring 1014 of each dummy composite structure 1012. In addition, a space-charge depletion region 1046 is formed along the junction between each n-well 1044 and the substrate material 1010. (A space-charge depletion region is formed whenever an n-type material is brought into contact with a p− type material.)

Next, as shown in FIG. 10E, after alternately patterned mask 1020 has been removed, a mask 1050 is formed and patterned on the top surface of substrate material 1010. Following this, the wafer is implanted with a p-type dopant to form a p-type ring 1052 that lies between each n− well 1044 and isolation ring 1014. As shown, the implant forms a number of RF blocking structures 1054, like RF blocking structures 512. Mask 1050 is then removed, followed by the conventional formation of metal interconnect structure 1030.

Alternately, as shown in FIG. 10F, after the p− type rings 1052 have been formed and mask 1050 has been removed, a mask 1060 can be formed and patterned on the top surface of p− substrate material 1010. Following this, the wafer is implanted with a p-type dopant to form a number of p+ structures 1062 so that a p+ structure 1062 lies inside each n− well 1044. The p+ structures 1062 can be formed as a grid (to form a number of RF blocking structures 612) or as a number of spaced-apart regions (to form a number of RF blocking structures 712). Mask 1060 is then removed, followed by the conventional formation of metal interconnect structure 1030.

Alternately, as shown in FIG. 10G, prior to the formation of substrate material 1010, a mask 1070 can be formed on the top surface of a conventionally-formed p− wafer material 1072. Following this, the wafer material 1072 is implanted with an n-type dopant to form a number of n+ structures 1074 that lie directly below where a metal bond pad, metal trace, or other RF structure is to be formed. The n+ structures 1074 can be formed as a number of spaced-apart regions (to form spaced-apart regions 812), or as a grid (to form grid 912). Mask 1070 is then removed.

Next, as shown in FIG. 10H, an n− epitaxial layer 1076 is conventionally grown on the top surface of p− wafer material 1072 to form n− substrate material 1010, followed by the conventional formation of the isolation rings 1014. After this, the structures of semiconductor dice 200, 300, 400, 500, 600, or 700 are formed in epitaxial layer 1076 as discussed above, followed by the conventional formation of metal interconnect structure 1030 to form, when singulated, a die 1080. As shown in FIG. 10I, die 1080 is identical to die 600 except that the conductivity types are reversed.

It should be understood that the above descriptions are examples of the present invention, and that various alternatives of the invention described herein may be employed in practicing the invention. Thus, it is intended that the following claims define the scope of the invention and that structures and methods within the scope of these claims and their equivalents be covered thereby. 

1. A method of forming a semiconductor structure in a semiconductor wafer, the method comprising: forming a semiconductor region in the semiconductor wafer, a top surface of the semiconductor region touching a top surface of the semiconductor wafer, the semiconductor region and the semiconductor wafer having opposite conductivity types; and forming a metal interconnect structure that touches the top surface of the semiconductor wafer directly vertically over all portions of the semiconductor region so that no electrically conductive structure touches any portion of the top surface of the semiconductor wafer that lies directly vertically over any portion of the semiconductor region.
 2. The method of claim 1 wherein the semiconductor region includes no region with a conductivity type that matches a conductivity type of the semiconductor wafer.
 3. The method of claim 2 and further comprising forming a non-conductive structure in the semiconductor wafer before the semiconductor region is formed, the non-conductive structure to laterally surround the semiconductor region.
 4. The method of claim 2 wherein: the semiconductor wafer has a substrate layer and an epitaxial layer that touches a top surface of the substrate layer; and the top surface of the semiconductor region touches a top surface of the epitaxial layer.
 5. The method of claim 4 and further comprising forming a conductive region in the substrate layer before the semiconductor region is formed, the conductive region and the substrate layer having opposite conductivity types, the semiconductor region lying directly vertically over the conductive region.
 6. The method of claim 1 and further comprising forming a doped region in the semiconductor region, a portion of the semiconductor region lying below the doped region, the doped region and the semiconductor region having opposite conductivity types, a top surface of the doped region touching the top surface of the semiconductor wafer.
 7. The method of claim 6 and further comprising forming a non-conductive structure in the semiconductor wafer before the semiconductor region is formed, the non-conductive structure to laterally surround the semiconductor region.
 8. The method of claim 6 wherein the top surface of the doped region divides the top surface of the semiconductor region into a number of laterally spaced apart sections.
 9. The method of claim 6 wherein the semiconductor region completely laterally surrounds the doped region.
 10. The method of claim 9 and further comprising forming a non-conductive structure in the semiconductor wafer before the semiconductor region is formed, the non-conductive structure to laterally surround the semiconductor region.
 11. The method of claim 6 wherein: the semiconductor wafer has a substrate layer and an epitaxial layer that touches a top surface of the substrate layer; and the top surface of the semiconductor region touches a top surface of the epitaxial layer, and further comprising forming a conductive region in the substrate layer before the semiconductor region is formed, the conductive region and the substrate layer having opposite conductivity types, the semiconductor region lying directly vertically over the conductive region.
 12. The method of claim 1 and further comprising forming a doped region in the semiconductor wafer, the doped region to touch and laterally surround the semiconductor region, the doped region and the semiconductor region having opposite conductivity types, a top surface of the doped region touching the top surface of the semiconductor wafer.
 13. The method of claim 12 and further comprising forming a non-conductive structure in the semiconductor wafer before the semiconductor region is formed, the non-conductive structure to laterally surround the semiconductor region, the doped region to touch the non-conductive structure and lie between the non-conductive structure and the semiconductor region.
 14. The method of claim 12 wherein: the semiconductor wafer has a substrate layer and an epitaxial layer that touches a top surface of the substrate layer; and the top surface of the semiconductor region touches a top surface of the epitaxial layer.
 15. The method of claim 14 and further comprising forming a conductive region in the substrate layer before the semiconductor region is formed, the conductive region and the substrate layer having opposite conductivity types, the semiconductor region lying directly vertically over the conductive region.
 16. The method of claim 1 and further comprising: forming a first doped region in the semiconductor wafer, the first doped region to touch and laterally surround the semiconductor region, the first doped region and the semiconductor region having opposite conductivity types, a top surface of the first doped region touching the top surface of the semiconductor wafer; and forming a second doped region in the semiconductor region, a portion of the semiconductor region lying below the second doped region, the second doped region and the semiconductor region having opposite conductivity types, a top surface of the second doped region touching the top surface of the semiconductor wafer.
 17. A method of forming a semiconductor structure in a semiconductor wafer, the method comprising: forming a semiconductor region in the semiconductor wafer, a top surface of the semiconductor region touching a top surface of the semiconductor wafer, the semiconductor region and the semiconductor wafer having opposite conductivity types; forming a metal interconnect structure that touches the top surface of the semiconductor wafer, the metal interconnect structure including a plurality of electrically conductive structures, no electrically conductive structure touching any portion of the top surface of the semiconductor wafer that lies directly vertically over any portion of the semiconductor region; forming a first doped region in the semiconductor wafer, the first doped region to touch and laterally surround the semiconductor region, the first doped region and the semiconductor region having opposite conductivity types, a top surface of the first doped region touching the top surface of the semiconductor wafer; and forming a second doped region in the semiconductor region, a portion of the semiconductor region lying below the second doped region, the second doped region and the semiconductor region having opposite conductivity types, a top surface of the second doped region touching the top surface of the semiconductor wafer, the first doped region touching the second doped region.
 18. The method of claim 16 wherein the semiconductor region completely laterally surrounds the second doped region.
 19. The method of claim 16 wherein: the semiconductor wafer has a substrate layer and an epitaxial layer that touches a top surface of the substrate layer; and the top surface of the semiconductor region touches a top surface of the epitaxial layer.
 20. The method of claim 19 and further comprising forming a conductive region in the substrate layer before the semiconductor region is formed, the conductive region and the substrate layer having opposite conductivity types, the semiconductor region lying directly vertically over the conductive region. 